A case is reported in a 6-year-old sterilized cat that presented with despondency and a 24-h history of vomiting and oedema of the face and neck. Examination revealed that the animal was lethargic and hypothermic; blood samples were brown in colour and contained numerous Heinz bodies. The cat was diagnosed with overdose of paracetamol [acetaminophen], which had been administered by its owners. The animal received perfusion, oxygen therapy and symptomatic treatment, but died 48 h after admission.